Specifications

Chapter 4 Restarting or Shutting Down a Computer 57
Manipulating Open Firmware NVRAM Variables
To manipulate Open Firmware NVRAM variables, use the nvram tool. If you modify a
value with
nvram, the value is saved only if the computer cleanly restarts or shuts down.
For more information, see the
nvram man page.
To view NVRAM variables:
$ nvram -p
Monitoring and Restarting Critical Services
In earlier versions of Mac OS X, a daemon called watchdog monitored critical services
and restarted them if they failed or quit unexpectedly after a computer restarted.
The
watchdog daemon relied on the configuration file watchdog.conf, located in /etc/.
In Mac OS X Server v10.4, watchdog was replaced by launchd. The launchd daemon
manages other daemons, both for the computer and for users. You can configure the
launchd daemon to launch other daemons on demand, based on criteria specified in
their respective XML property lists.
During system startup, launchd is the first process invoked by the kernel to run and set
up the computer. In Mac OS X Server, it is preferable to have your daemon started by
launchd.
Note: Some system administrators must modify the boot process to insert a script or
implement a change in the default system configuration. System administrators are
encouraged to work with launchd to implement changes, and avoid modifying rc or
creating a SystemStarter Startup Item. The rc command script might be phased out in
the future.
The configuration files are in the following folders:
Folder Usage
/System/Library/LaunchAgents/ Configuration for the system
/System/Library/LaunchDaemons/ Configuration for the daemons
~/Library/LaunchAgents/ Configuration per user